The present disclosure relates generally to information handling systems, and more particularly to the use of stubs on differential trace pairs in an information handling system in order to reduce crosstalk between adjacent differential trace pairs.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Many information handling systems include high speed buses for routing information, and as speeds have increased, transmission line routing imperfections that were previously considered low risk have become an issue. For example, high speed information transmission typically uses differential signaling techniques that operate to transmit information from a sender device using two complementary signals that provide the same signal as a “differential pair” of traces that are provided on a circuit board and that reference each other. The receiving device responds to the electrical differences between the two signals provided using such differential trace pairs, rather than the difference between a single trace and ground (a technique called single-ended signaling). The use of differential trace pairs has traditionally minimized crosstalk and electromagnetic interference (both noise emission and noise acceptance), and can achieve a constant or known characteristic impedance, which allows for impedance matching techniques that allow for high speed transmissions of information over the differential trace pairs.
However, as the transmission speeds over such differential trace pairs have increased, problems associated with crosstalk has become more and more prevalent. Crosstalk is a phenomenon in which signal integrity is compromised when adjacent differential trace pairs are switching and noise from one differential trace pair couples to an adjacent differential trace pair. For example, microstrip structures (e.g., differential trace pairs routed on a top or bottom layer of a printed circuit board) are known to exhibit high amounts of far-end crosstalk, and have resulted in most high speed signal routing on circuit boards utilizing stripline structures (e.g., differential trace pairs routed within the circuit board between its top and bottom surface.) However, the use of stripline structures can lead to an increase in the number of signal layers in the circuit board and the resulting increases in circuit board cost. In order to avoid crosstalk, differential trace pairs are typically spaced as far apart as possible (e.g., a general rule is to space them by a distance of at least five times the thickness of their dielectric), but as circuit boards become denser and/or circuit board costs reduction becomes desirable, differential trace pairs have been positioned closer and closer to each other on the circuit board (in both microstrip and stripline structure). At such relatively close spacing, both microstrip and stripline structures exhibit increases in crosstalk.
Accordingly, it would be desirable to provide for improved crosstalk performance for high speed differential pair traces.